1. Field of the Invention
The invention relates to a liquid-filled type vibration isolating apparatus, and in particular, to a vibration isolating apparatus in which the characteristic of isolating vibration is improved by controlling the internal pressure of a liquid chamber.
2. Description of the Related Art
An automobile engine is supported to a vehicle body via a vibration isolating apparatus. The vibration of the engine is prevented from being transmitted to the vehicle body.
Such vibration isolating apparatus includes a liquid-filled type vibration isolating apparatus in which a liquid chamber is provided within the apparatus and vibration is effectively absorbed at the time of input of vibration by controlling the internal pressure of the liquid chamber.
In the liquid-filled type vibration isolating apparatus, a movable plate, which can be moved by an actuator such as an electromagnet, is provided at a partitioning member which faces the pressure-receiving liquid chamber . The internal pressure of the pressure-receiving liquid chamber is controlled by vibrating the movable plate in accordance with the input of vibration.
The movable plate is resiliently supported by an elastic body such as a metallic spring, rubber, and the like. In a system in which the movable plate is supported by the metallic spring, a partitioning member is formed of a thin metallic plate and the partitioning member itself serves as the metallic spring and supports the movable plate. Further, the movable plate and the partitioning member are adherently fixed so as to prevent the leakage of the liquid.
On the other hand, in a system in which the movable plate is supported by the rubber, an annular rubber is connected to the outer periphery of the movable plate and the outer periphery of the rubber is connected to the partitioning member.
However, in the system in which the movable plate is supported by the rubber, the length of the rubber in the direction orthogonal to the displacing direction of the movable plate is short, and the spring constant of the rubber in the displacing direction of the movable plate is as relatively high as that of a metallic spring. As a result, distortion of the rubber at the time of control becomes large and durability of the rubber deteriorates.
Moreover, in the system in which the metallic spring serves as the partitioning member and supports the movable plate, the stress applied to the partitioning member is concentrated on a stationary portion thereof at the time of control and cracking may occur at the partitioning member.